In the past controllable outlet nozzles constructed as pneumatic constriction nozzles have been used in pneumatic dosaging conveyors for conveying fine material with a high degree of precision. Their control range is very limited at the usual operational gas pressures (about 20%). This control range is not sufficient for many new technological processes (for instance when a plurality of products are to be mixed in a common conveying pipe with a high degree of precision using the smallest possible quantity of gas).